This invention relates to regulation of the uniformity of textile sliver drafted by sliver drafting apparatuses, and more specifically relates to regulation of the uniformity of the sliver drafted during certain of operation, including particularly periods of start-up, of the drafting apparatuses.
It is known to provide sliver drafting apparatuses with so-called "leveler" mechanisms adapted to detect variations in the uniformity of the sliver drafted by the apparatuses and to correctively vary the draft imparted to the sliver in proportion to the detected uniformity variations. One leveler mechanism of the aforesaid type is that heretofore manufactured and sold by Platt Saco Lowell Corporation and disclosed in its publication entitled "INSTRUCTION MANUAL VERSAMATIC.RTM. MODEL DF DRAWING FRAME." Other known prior art of possible relevance to the present invention includes U.S. Pat. Nos. 2,812,553, 3,435,673, 3,673,591, 3,744,093, 3,822,590 and 3,869,759.
Leveler mechanisms of the above-described type generally function quite well during regular operation of the drafting apparatuses with which they are associated. However, at least some do not function satisfactorily during periods of start-up of the apparatuses, due to then existing instability of the means they employ for detecting variations in the sliver uniformity. For example, the detecting means of the hereinbeforenoted leveler mechanism of Platt Saco Lowell Corporation, which utilizes pneumatic principals in its detection of sliver uniformity variations, stabilizes only after some four to five seconds of start-up operation of the drafting apparatus. Such a leveler mechanism may cause grossly improper changes in the draft imparted to the sliver during start-up of a drafting apparatus if permitted to then function. In recognition of the foregoing fact, it has heretofore been proposed to null the operation of the leveler mechanism during each period of start-up of the drafting apparatus. This solution to the problem is not entirely satisfactory. It affords no correction whatsoever of any uniformity variations present within the sliver drafted by the apparatus during each start-up period: At current production rates, over 100 feet of sliver may pass through the apparatus during each such five-second time period. An alternative solution which might at first impression appear feasible would be to subject the sliver drafted during apparatus start-up to the same correction draft as was being applied to the sliver at the time the apparatus was shut-down. However, this is also unsatisfactory. Shut-down of a drafting apparatus is commonly caused by one or more of the strands in the sliver array breaking, running-out, or lapping-up about a drafting roll of the apparatus. The leveler mechanism may detect the marked change in uniformity, resulting from the absence of one or more of the sliver strands, prior to the drafting apparatus being shut-down, either manually or by actuation of one of the stop-motion devices customarily associated with the drafting apparatus. In this situation the correction draft produced by the leveler mechanism at the time of shut-down will be of a large positive magnitude adapted to offset the grossly underweight condition of the sliver attributable to the incomplete nature of its array. While the drafting apparatus is shut-down, a machine attendant should and normally would restore the sliver array to its complete condition. Upon subsequently ensuing start-up of the apparatus, it would therefore be inappropriate and detrimental to apply to the restored array of sliver the same correction draft as was applied to the imcomplete sliver array at the time of shut-down of the apparatus: If done, this would cause the sliver processed by the apparatus during the period of start-up to be severely overweight.
The initial and terminal parts of each period of start-up of the drafting apparatus present still other considerations. For approximately the first second of each period of start-up thereof, the drafting apparatus is rapidly accelerating to full operating speed. If the leveler mechanism acheives draft correction by causing absolute-value changes in the speed of certain of the drafting rolls, a speed change of any given absolute value will not produce the same correction draft while the apparatus is accelerating as it would produce if the apparatus were operating at full speed. The terminal part of each period of start-up of the apparatus is significant since it is one of transition: The leveler mechanism, which during start-up has not been permitted to function in its normal manner, will now again do so. The resumption of normal operation of the leveler mechanism should preferably be effected, at this time of transition, in a way allowing the leveler mechanism to rapidly but smoothly apply to the sliver then passing through the drafting apparatus correction drafts proportional to whatever uniformity variations are actually present within such sliver.